Prostheses of this type are conventionally made with or without central stems. The presence of such a stem, which generally is cemented to the bone, affords greater stability but does not by itself prevent buckling in a plane perpendicular to the swing axis of the jacket; its insertion, furthermore, often necessitates the resection of much healthy bone tissue. Many of the existing prostheses, moreover, require extensive surgical operations when a worn part is to be replaced.